The present invention relates to the nuclear medicine art. It finds particular application in conjunction with gamma cameras for positron and single photon imaging and will be described with particular reference thereto. It will also be appreciated that the present invention finds application to non-invasive inspection, industrial testing, and like applications.
Traditional nuclear cameras have included one or more radiation sensitive detectors. In single photon emission computed tomography (SPECT) systems, the detectors have been mounted for rotation about an examination region. As the detectors are rotated around the subject or indexed to a multiplicity of angularly offset positions around the subject, a tomographic data set indicative of a plurality of radionuclide decays occurring within the examination region is collected. This collected data is used to create a human-readable image indicative of the radionuclide spatial and temporal distribution.
Positron emission tomography (PET) scanners typically include ring of radiation sensitive detectors surrounding a central examination region. Positron annihilation events occurring within the examination region generate 511 keV gamma ray pairs travelling in opposite directions along a line of coincidence. Coincident gamma ray pairs detected by the ring of detectors are used to generate a human readable image indicative of the positron annihilation events.
More recently, gamma cameras capable of detecting both single photon radiation and positron annihilation events have been introduced. These cameras typically include a relatively thicker scintillator so that the 511 keV gamma rays characteristic of positron annihilation events can be more efficiently detected. Moreover, such cameras typically include coincidence logic for determining whether events are detected by two detectors substantially simultaneously.
While the foregoing devices have proven clinically and commercially successfiul, there remains room for improvement. For example, an increasing emphasis on improved imaging coverage and reduced imaging time leads to detector arrangements having a tunnel effect which limits access to the object under examination and which can be disconcerting to human patients. Moreover, ingress to and egress from such systems can be difficult. Dedicated PET scanners have been relatively expensive and confined to producing images indicative of relatively limited axial extent. Depending on the axial range over which data must be collected, it is often necessary to index the object with respect to the detectors and repeat the data collection procedure.
One factor affecting the quality of nuclear images has been non-uniform radiation attenuation in the object under examination. For example, some of the gamma radiation indicative of radionuclide decays occurring within the anatomy of a patient may travel through relatively attenuative material such as bone, whereas some of the radiation may not. If not corrected, this non-uniformity can result in undesirable image artifacts. As a result, gamma cameras have included transmission radiation sources. The transmission data has been used to generate attenuation maps of the object under examination. The attenuation maps have in turn been used to correct the received emission data.
However, coordination of single photon imaging with positron coincidence imaging has proven difficult. One alternative has been to obtain successive transmission and emission scans. Drawbacks to this approach include increased imaging time and possible misregistration of the transmission and emission date due to patient movement. Positron coincidence and transmission data have also been collected simultaneously. A drawback to this approach is the complexity inherent in operating a gamma camera in both single photon and coincidence modes simultaneously.
Those skilled in the art will, upon reading and understanding the appended description, appreciate that aspects of the present invention address these and other matters.
According to a first aspect of the present invention, a gamma camera includes a fixed detector having a radiation sensitive face which faces an examination region and a movable second detector. The second detector includes a plurality of discrete detector portions each having a radiation sensitive face which faces the examination region. The second detector is movable between a first position opposite the examination region from the fixed detector for detecting radiation from the examination region and a second position for facilitating ingress of an object into the examination region.
According to a more limited aspect of the present invention, the discrete detector portions include an elongate scintillator, a plurality of photodetectors disposed along a first edge of the scintillator, and a plurality of photodetectors disposed along a second edge of the scintillator. The second edge of the scintillator, is opposite the first edge.
According to a still more limited aspect of the present invention, the elongate scintillator comprises a plurality of scintillator layers. The gamma camera includes photodetector means for detecting scintillations occurring in each of the layers.
According to another more limited aspect of the present invention, the gamma camera includes first and second moment processors operatively connected to the photodetectors for determining x,y positions of the scintillations.
According to another limited aspect, the gamma camera includes a transmission radiation source which emits radiation which interacts with the second detector to produce Compton scattered photons. At least a portion of the photons pass through the examination region and are received by the first detector. In its first position, the second detector is disposed between the transmission source and the examination region.
According to a more limited aspect, the gamma camera includes means for translating the transmission radiation source along each of the discrete detector portions.
According to a more limited aspect, the transmission radiation source includes one of 133-Ba and 137-Cs.
The gamma camera may also include a coincidence detector for determining whether radiation detected by the fixed detector and the detector portions of the second detector is coincident.
The gamma camera may also include a pressure sensitive surface disposed between the fixed detector and examination region which surface provides a signal indicative of a pressure applied to the surface. Means for determining a region of the object which can be modeled as a uniform medium and means for generating an attenuation map of a second region of the object can also be included.
According to another aspect of the present invention, a gamma camera includes a first detector having a radiation sensitive face which faces an examination region and a second detector disposed opposite the examination region from the first detector. The second detector includes a first radiation sensitive face which faces the examination region and a second radiation sensitive face. The camera also includes a transmission radiation source for emitting transmission radiation which is received by the second radiation sensitive face of the second detector, said transmission radiation interacting with the second detector to produce Compton scattered photons which are received by the first detector. Means for determining whether transmission radiation received by the second detector and Compton scattered photons received by the first detector are coincident is also included.
According to a more limited aspect, the second detector may include a plurality of elongate detector portions disposed in an arc about the examination region. The detector portions include a scintillator and a plurality of photodetectors for receiving light which has reached first and second edges of the scintillator.
The second detector may also include a scintillator having a plurality of layers and a plurality of photodectors for receiving signals indicative of scintillations occurring in each of the layers. The gamma camera further includes means for selectively disregarding signals from at least one of the layers during operation of the transmission radiation source.
According to a yet more limited aspect of the invention, the gamma camera may include a first scintillator layer disposed between a pair of light reflective surfaces which cause light generated within the crystal to be reflected to an edge thereof.
The gamma camera may include means for disregarding signals from a scintillator layer nearest the examination region while accepting signals from a layer nearest the transmission source.
According to another limited aspect of the invention, the second detector may be movable between a first position for detecting radiation from the examination region and a second position for facilitating ingress of an object into the examination region.
According to a still more limited aspect, the gamma camera may include means for scanning the transmission source across the second radiation sensitive face of the second detector when the second detector is in the first position.
According to a yet more limited aspect, the gamma camera may include means for scanning the transmission source longitudinally with respect to the examination region when the second detector is in the second position.
According to another aspect of the present invention, a method includes using a fixed radiation sensitive detector to detect gamma radiation from an examination region, using a second detector to delete gamma radiation from the examination region, determining whether the radiation detected by the first and second detectors is indicative of positron annihilation events, and generating an image indicative of the detected positron annihilation events. The second detector includes a plurality of discrete detector portions each having a first radiation sensitive face which faces the examination and is movable between a first position for detecting radiation from the examination region and a second position for facilitating ingress of an object into the examination region.
According to a limited aspect of the invention, the discrete detector portions include a second radiation sensitive face. The method includes the steps of providing transmission radiation which is received by the second radiation sensitive face of a discrete detector portion, said transmission radiation interacting with the discrete detector portion to produce Compton scattered photons which interact with the first detector, using the discrete detector portion to detect the interactions, using the first detector to detect radiation incident thereon, determining whether radiation received by the discrete detector portion and Compton scattered photons received by the first detector are coincident, and using the coincident radiation to provide an attenuation corrected image of the detected positron annihilation events.
The method may include repeating the steps of providing, using the discrete detector portion, using the first detector, and determining for a plurality of the discrete detector portions.